High current bi-polar pulse system for use in electrochemical metal surface finishing

Abstract

A high current bi-polar pulse system for use in electrochemical metal surface finishing of metallic components. The high current bi-polar pulse system provides a high isolation, high current switching device for providing independently controllable, alternating polarity, variable time duration pulses for electrochemical and mechanical finishing of metallic components in a conducting fluid bath. The high current bi-polar pulse system provides a safe, low-cost solution for implementing the surface finishing of niobium (Nb) SRF accelerating cavities without the use of hydrofluoric acid.

1 . An apparatus for electropolishing a superconductive radio frequency cavity comprising:
 a cathodic voltage source comprising a first variable direct current power supply and a first capacitor bank in electrical communication with said first variable power supply;   an anodic voltage source comprising a second variable direct current power supply and a second capacitor bank in electrical communication with said second variable power supply;   a counter-electrode at least partially disposed in an electrolytic fluid which is in contact with a niobium cavity to be polished;   a first conductive path between said cathodic voltage source and said counter electrode;   a second conductive path between said anodic voltage source and said counter electrode;   a cathodic voltage switch positioned within the conductive path between said cathodic voltage source and said counter-electrode;   an anodic voltage switch positioned within the conductive path between said anodic voltage source and said counter-electrode; and,   a timing control circuit disposed to control the operation of said voltage switches.   
     
     
         2 . The apparatus for electropolishing a superconductive radio frequency cavity of  claim 1  wherein each of said first and second variable direct current power supplies is independently adjustable. 
     
     
         3 . The apparatus for electropolishing a superconductive radio frequency cavity of  claim 2  wherein each of said first and second variable direct current supplies is a high current power source and supplies between four and twenty volts. 
     
     
         4 . The apparatus for electropolishing a superconductive radio frequency cavity of  claim 3  wherein each of said first and second variable direct current supplies provides twenty volts. 
     
     
         5 . The apparatus for electropolishing a superconductive radio frequency cavity of  claim 1  wherein said apparatus does not include a rectifier. 
     
     
         6 . The apparatus for electropolishing a superconductive radio frequency cavity of  claim 1  wherein each of said first and second capacitor banks provides ten farads or greater electrical capacitance. 
     
     
         7 . The apparatus for electropolishing a superconductive radio frequency cavity of  claim 1  wherein each of said switching device is a fast switching, low impedance semi-conductor device. 
     
     
         8 . The apparatus for electropolishing a superconductive radio frequency cavity of  claim 7  wherein each of said switching devices is an insulated-gate bi-polar transistor. 
     
     
         9 . An apparatus for electropolishing a superconductive radio frequency cavity comprising:
 at least two direct current power supplies;   at least two capacitor banks; each capacitor bank connected to a separate direct current power supply;   a counter electrode connected to said capacitors via a conduction pathway; said counter electrode being in communication with an electrolytic fluid and said fluid being in contact with a surface of niobium cavity;   at least two switching devices positioned to regulate the conduction pathway between said capacitors and said counter electrode; and,   a timing control circuit disposed to operate said at least two switching devices.   
     
     
         10 . A method of chemically processing a metallic work piece comprising the steps of:
 providing a source of cathodic voltage comprising a first direct current power supply and at least one first capacitor providing at least ten farads electrical capacitance and a source of anodic voltage comprising a second direct current power supply and at least one second capacitor providing at least ten farads electrical capacitance;   connecting said sources of cathodic voltage and anodic voltage via a respective conduction path to an electrochemical cell comprising a metallic work piece, a counter electrode, and an electrically conducting fluid; and,   using a timing control circuit to alternate discharge of said at least one first capacitor and said at least one second capacitor according to a predetermined programmed sequence.   
     
     
         11 . The method of  claim 10  wherein each said conduction path incorporates an electronic switch. 
     
     
         12 . The method of  claim 11  wherein each said electronic switch further comprises an insulated-gate bipolar transistor. 
     
     
         13 . The method of  claim 12  wherein said insulated-gate bipolar transistors provide an at least five hundred amperes conduction path from said sources of cathodic voltage and anodic voltage through the electrochemical cell. 
     
     
         14 . The method of  claim 10  further comprising independently adjusting the output of each of said first and second power supplies in order to assist in generating the desired cathodic voltage and anodic voltage in the system.